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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [SimplifyCFG] Chain of comparisons no longer flattened"
href="https://bugs.llvm.org/show_bug.cgi?id=51211">51211</a>
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<th>Summary</th>
<td>[SimplifyCFG] Chain of comparisons no longer flattened
</td>
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<th>Product</th>
<td>libraries
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Scalar Optimizations
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>nikita.ppv@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>lebedev.ri@gmail.com, llvm-bugs@lists.llvm.org
</td>
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<p>
<div>
<pre>For the following Rust code:
pub struct Blueprint {
pub fuel_tank_size: u32,
pub payload: u32,
pub wheel_diameter: u32,
pub wheel_width: u32,
}
impl PartialEq for Blueprint{
fn eq(&self, other: &Self) -> bool {
self.fuel_tank_size == other.fuel_tank_size
&& self.payload == other.payload
&& self.wheel_diameter == other.wheel_diameter
&& self.wheel_width == other.wheel_width
}
}
LLVM 12 managed to compile this to a nice <4 x i32> comparison, while in LLVM
13 this is a sequence of i32 comparisons with two branches sitting in between.
Here is an end-to-end IR test case: <a href="https://llvm.godbolt.org/z/59cT1coT6">https://llvm.godbolt.org/z/59cT1coT6</a>
The relevant difference is that SimplifyCFG no longer fully flattens the
control flow in this case.
Here is just the -simplifycfg part: <a href="https://llvm.godbolt.org/z/zfd9Ybx58">https://llvm.godbolt.org/z/zfd9Ybx58</a>
I haven't checked what change caused this yet.</pre>
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